Polyvinyl alcohol (PVOH) is a water soluble, repulpable and biodegradable resin with excellent aroma and oxygen barrier properties and resistance to most organic solvents. Other desirable attributes of PVOH include anti-static properties, grease and oil resistance and heat sealability. The polymer is used extensively in adhesive, textile sizing and paper coatings. However, the end uses of PVOH have been limited despite its excellent chemical, mechanical and physical properties to those uses in which it is supplied as a solution in water. This limitation is partly due to the fact that vinyl alcohol polymers in the unplasticized state have a high degree of crystallinity and show little or no thermoplasticity before the occurrence of decomposition which starts at about 170.degree. C. and becomes pronounced at 200.degree. C., which is below its crystalline melting point.
With the present public concern for preserving the environment, it has been found desirable to search for materials which, when disposed after use, will physically or biologically decompose and thereby avoid polluting the environment. One candidate for such a material is water-soluble PVOH.
U.S. Pat. No. 5,051,222 discloses a method for making thermoplastic (melt extrudable) PVOH compositions which comprises providing sufficient energy to a PVOH which is at least partially crystalline to both melt the PVOH and substantially eliminate the crystallinity in the PVOH melt while simultaneously removing energy from the PVOH melt at a rate sufficient to avoid decomposition of the PVOH. The melt is then extruded, preferably into a strand, rapidly cooled and cut into pellets for subsequent thermoprocessing into the desired product or article.
As a result of the availability of such thermoplastic PVOH compositions, the desirable physical and mechanical properties of PVOH such as biodegradability, water solubility and repulpability have opened new market opportunities for PVOH, especially in packaging applications where the contents must be dissolved or dispersed in water. Examples of such packaging applications for PVOH film include pesticides which are applied as a water spray, caustic cleaners or detergents which are dissolved during use, and process chemicals such as pigments, dyes or carbon black which are dissolved or dispersed in water. The advantages of using a water soluble film for packaging the above materials include the elimination of both human exposure to highly toxic or concentrated chemicals and the need to clean and discard contaminated chemical containers after use.
PVOH films can also be used to control contamination in hospitals. Soiled laundry can be collected and placed directly into a PVOH bag. The bag is then placed into the washing machine where the bag dissolves completely.
Examples for molding applications include disposable sanitary products such as tampon insertion tubes or vials for solvent based chemicals.
U.S. Pat. No.5,095,054 discloses a thermoplastic polymer composition comprising a destructured starch and a thermoplastic polymer.